The invention relates generally to an apparatus and a method for treating cardiac arrhythmia or fibrillation, and more particularly, to a defibrillator system that employs high-frequency, high-energy pulses to correct arrhythmia or fibrillation.
Throughout this specification, the term xe2x80x9cpulsexe2x80x9d is used to describe a signal having an on duration during which a waveform having an appreciable voltage level is present. The waveform defining the pulse may be a dc waveform, e. g., a discharge curve of a capacitor, or a symmetric waveform, e. g., a sine wave.
Electrical energy is applied to patients for many reasons, two of which are to ablate cardiac tissue and to defibrilate the heart. In ablation, energy is applied to cause targeted tissue to increase in temperature until the tissue is no longer viable. This approach is taken in terminating arrhythmias of the heart. It has been found that applying ablation energy having a substantial dc component can cause the heart to fibrillate.
As is known to those skilled in the art, xe2x80x9cfibrillationxe2x80x9d is a condition in which individual muscle fibers quiver or spontaneously contract. In an atrium of the heart, it is indicated by extremely rapid, incomplete contractions of the atria resulting in fine, rapid, irregular, and uncoordinated movements. In a ventricle, it is a condition resulting in rapid, tremulous, and ineffectual contractions of the ventricles. In both cases, the heart is unable to pump necessary amounts of blood to sustain the patient. Fibrillation is to be avoided and thus, avoiding the application of energy with a substantial dc component to a non-fibrillating heart is recommended.
Defibrillator systems deliver a high voltage electrical counter shock to the heart in an attempt to correct or convert a detected cardiac arrhythmia or fibrillation. The typical defibrillator system includes a capacitor system that produces a pulse defined by a trapezoidal or exponential decay waveform. This pulse is delivered to the heart through electrodes. It is hoped that such a counter shock will allow the heart""s normal pacemaker to take over.
A defibrillator system may be an external or internal device. An external defibrillator system applies energy to a patient through electrode pads. In an external defibrillator, a shock wave of approximately 200-400 joules is discharged across the chest through a pair of electrode pads positioned on the chest. An internal defibrillator system applies energy through an implanted device that includes a capacitor having leads terminating in the heart. In an internal defibrillator, a shock wave of approximately 40-80 joules is discharged through the heart.
In a typical defibrillator system, the pulses applied to the heart may be in the form of a monophasic or a biphasic pulse. As shown in FIG. 1, monophasic pulses comprise a single monotonically decaying electrical waveform that is typically truncated before the defibrillator capacitor system is completely discharged. The monophasic pulse comprises a substantial dc component. As shown in FIG. 2, a biphasic pulse comprises a pair of decaying electrical waveforms or phases that are of opposite polarity. As indicated in FIG. 2, the biphasic waveform is a non-recurrent, asymmetric waveform having unequal positive and negative portions. Accordingly, the biphasic pulse retains a substantial dc component. To generate a biphasic pulse, a first pulse or phase is discharged from a capacitor system in the same manner as a monophasic pulse and, at the point the first pulse is truncated, a switch circuit connected to the electrodes is used to immediately reverse the discharge polarity of the capacitor system as seen by the electrodes in order to produce the second waveform or phase of the biphasic pulse that is of the opposite polarity.
For either the monophasic or biphasic pulses, the pulse applied to the heart has a substantial dc component. However, it has been found that the application of dc current through the heart causes significant pain to the patient undergoing defibrillation. Therefore, it would be beneficial to a patient if a defibrillation pulse did not contain any appreciable dc component, yet still included enough energy to defibrilate the heart.
Hence, those skilled in the art have recognized a need for a defibrillator system that corrects or converts a detected cardiac arrhythmia or fibrillation in a way less painful than currently available defibrillator systems. The invention fulfills these needs and others.
Briefly, and in general terms, the invention is directed to an apparatus and a method for correcting or converting a detected cardiac arrhythmia or fibrillation.
In a first aspect, the invention is related to a method of applying energy to a heart, including defribrilating a heart that is in fibrillation. The method includes the step of applying, across the heart, a pulse comprising a high-frequency cyclic waveform having a plurality of cycle groups. The waveform has, during the first cycle group, an initial peak-to-peak voltage sufficient to shock the heart and, during each subsequent cycle group, a subsequent peak-to-peak voltage, the pulse substantially lacking a dc component. The method further includes the step of controlling the total energy delivered to the heart.
In a more detailed aspect of the method, each cycle group comprises at least one cycle of the cyclic waveform. In another aspect, each cycle group has a peak-to-peak voltage less than that of the previous cycle group. In yet another facet, the profile of the cyclic waveform resembles a discharge curve of a capacitor. In another, the initial peak-to-peak voltage of the cyclic waveform and each subsequent peak-to-peak voltage are substantially equal. In further aspects, when the pulse is applied external to the heart, the initial peak-to-peak voltage is between approximately 9000 volts and 10,000 volts and, when the pulse is applied internal to the heart, the initial peak-to-peak voltage is between approximately 1000 volts and 1200 volts. In still other aspects, the total energy is controlled by varying the peak-to-peak voltages and/or by varying the time duration of pulse.
In second aspect, the invention is related to a method of applying a high-energy, high-frequency pulse across a heart for restoring effective cardiac rhythm. The method includes the steps of charging a capacitor having a first terminal and a second terminal to an initial voltage level sufficient to shock the heart, applying the potential at the first terminal of the capacitor to a first cardiac-tissue contact point and applying the potential at the second terminal of the capacitor to a second cardiac-tissue contact point. The method further includes the steps of initiating the discharge of the capacitor and periodically interchanging the potentials at the first and second terminals of the capacitor during discharge of the capacitor to produce a waveform comprising a plurality of cycles each having a positive portion and a negative portion, the waveform substantially lacking a dc component.
In a detailed aspect of the method, the potentials are interchanged at fixed time intervals such that the cycles of the waveform have positive and negative portions of substantially equal time duration. In another aspect of the method, the potentials are interchanged until the capacitor is completely discharged. In another detailed facet of the method, the potentials are interchanged such that the cumulative energy of the positive portions is substantially equal to the cumulative energy of the negative portions. In another aspect, the potentials are interchanged such that, for each cycle, the energy in the positive portion is substantially equal to the energy in the negative portion. In a further aspect, the time duration of one portion of each cycle is greater than the time duration of the other portion of the same cycle. In still another facet, for each cycle, except the last, the potentials are interchanged such that the time duration of the positive portion is substantially equal to the time duration of the negative portion, and for the last cycle, the time duration of the second portion is such that the energy of the second portion is substantially equal to the summation of the energy differences between the positive and negative portions of each preceding cycle and the energy of the first portion of the last cycle.
In a third aspect, the invention is related to an apparatus for applying a high-energy, high-frequency pulse of energy across a heart for restoring effective cardiac rhythm. The apparatus includes a capacitor having a first terminal and a second terminal, a battery for charging the capacitor to an initial voltage level sufficient to shock the heart, a first electrode for contacting a first cardiac-tissue contact point and a second electrode for contacting a second cardiac-tissue contact point. Both the first and second electrodes are responsive to one of either the first or second terminals of the capacitor. The apparatus further includes a switching circuit for connecting the first electrode to the first terminal of the capacitor and the second electrode to the second terminal of the capacitor and periodically interchanging the connections, and a controller for controlling the switching circuit during discharge of the capacitor to produce a waveform comprising a plurality of cycles each having a positive portion and a negative portion, the waveform substantially lacking a dc component.
In a fourth facet, the invention pertains to an apparatus for applying a high-energy, high-frequency pulse across a heart for restoring effective cardiac rhythm. The apparatus includes a waveform generator for producing a high-frequency cyclic waveform comprising a plurality of waveform cycles and a controller responsive to the cyclic waveform for outputting a high-energy pulse comprising a plurality of substantially complete waveform cycles, at least one waveform cycle having a peak-to-peak voltage sufficient to shock the heart. The apparatus further includes a first electrode for contacting a first cardiac-tissue contact point, the first electrode responsive to the controller and a second electrode for contacting a second cardiac-tissue contact point, the second electrode responsive to a substantially constant potential.
In a detailed aspect of the apparatus, the cyclic waveform is a symmetric waveform, i.e., sine wave, square wave, etc. In another aspect, the at least one waveform has a peak-to-peak voltage of between approximately 1000 volts to 1200 volts. In yet another facet, the frequency of the cyclic waveform is between approximately 10 kHz and 500 kHz. In another aspect, the controller controls the total energy delivered to the tissue by varying the peak-to-peak voltage of the cyclic waveform and/or by varying the time duration of the pulse.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.